As mobile data applications are exponentially growing, to ensure network access experience of a large quantity of users, spectrum utilization per unit area of an existing wireless system needs to be greatly increased through the breakthrough development of wireless technologies. Therefore, a massive multiple-input multiple-output (Massive Multiple-input Multiple-output, Massive MIMO for short) system technology is introduced. The technology is considered one of key technologies of a fifth-generation mobile wireless communications system. Specifically, in a massive multiple-input multiple-output system, a base station is equipped with antennas of one order of magnitude more than those in an existing system, for example, hundreds of antennas.
The use of the massive multiple-input multiple-output technology can greatly improve spectrum utilization and system power efficiency, but during the use of the massive multiple-input multiple-output system, interference is a fundamental bottleneck limiting performance of the system. In the massive multiple-input multiple-output system, inter-cell interference (Inter-cell interference, ICI for short) exists between different base stations.
In a conventional cellular wireless system, a method for cancelling inter-cell interference is frequency reuse, but this method has relatively low spectrum utilization, and cannot meet a requirement of a next-generation wireless communications system. To improve spectrum utilization, a coordinated multi-point transmission (Coordinated Multi-Point Transmission, CoMP for short) technology is used in the next-generation wireless communications system. CSI (Channel State Information, channel state information) needs to be exchanged between base stations to implement this technology. In a process in which base stations exchange CSI, because a delay exists on a backhaul, CSI of other base stations obtained by a base station by using a backhaul connection is not exactly the same as current CSI of these base stations, which causes an error in the CSI obtained by the base station. Therefore, performance of CoMP is degraded. A greater delay on the Backhaul results in a greater error in the CSI obtained by the base station and poorer performance of CoMP. That is, CoMP is very sensitive to a backhaul delay. In the massive multiple-input multiple-output system, there is an urgent need to design an inter-cell interference cancellation solution that is not sensitive to a backhaul delay.